Apparatus for diffusion into semiconductor wafers

Abstract

In diffusing an impurity into semiconductor wafers within a silica tube by the use of a heating furnace, a method of diffusion involves the following steps: the semiconductor wafers are inserted into the tube from an inlet thereof, the inlet is sealed by a cap, the interior of the tube is placed under vacuum, and an atmosphere of the impurity is formed. Since, at heating, the tube is closed and no inert gas is fed thereinto, the temperature distribution within the tube is held uniform, and hence the quantities of impurity introduction into the semiconductor wafers are not varied.

What is claimed is: 
     
       1. An apparatus for treating semiconductor wafers comprising an elongated furnace tube having first and second openings, detachable closure means provided at said first opening for furnace tube having first and second openings, detachable closure means provided at said first opening for sealing said first opening, first supporting means for placing substantially erect semiconductor wafers into said tube to extend serially in a group along the axis of said tube and for arranging at least one boron nitride source substantially vertically relative to said semiconductor wafers in said tube and spaced from, but adjacent to, said semiconductor wafers without contacting the inner surface of said tube, means connected to said second opening for reducing pressure in said tube below atmospheric pressure, and means for heating said semiconductor wafers and boron nitride source so as to deposit boron impurity on surfaces of said semiconductor wafers from the boron nitride source under the pressure-reduced state, wherein said boron nitride source comprises at least one boron nitride wafer. 
     
     
       2. An apparatus according to claim 1, wherein said closure means includes means for moving said first and second supporting means inside said tube after sealing by said closure means. 
     
     
       3. An apparatus according to claim 1, wherein said impurity source includes a cylinder surrounding said group of semiconductor wafers. 
     
     
       4. An apparatus according to claim 3, wherein said semiconductor wafers are constituted by silicon, and said cylindrical impurity source is constituted by boron nitride. 
     
     
       5. An apparatus according to claim 1, wherein second detachable closure means are provided for sealing said second opening, said pressure reducing means being connected to the interior of said tube through said second closure means. 
     
     
       6. An apparatus according to claim 1, wherein said pressure reducing means reduces pressure in said tube below 100 torr. 
     
     
       7. An apparatus according to claim 6, wherein the pressure in said tube is reduced to 0.1 to 1.0 torr. 
     
     
       8. An apparatus according to claim 1, wherein said closure means provides an air-tight seal of said first opening. 
     
     
       9. An apparatus according to claim 1, wherein said first and second supporting means are integrally combined. 
     
     
       10. An apparatus for diffusing boron impurity into semiconductor wafers which comprise an elongated sealing said first opening, first supporting means for erecting semiconductor wafers in said tube along the length of said tube, second supporting means for arranging at least one impurity source containing a conductivity type determining impurity perpendicular to said semiconductor wafers in said tube spaced from, but adjacent to, the edges of said semiconductor wafers without contacting said tube, means connected to said second opening for reducing pressure in said tube below atmospheric pressure, and heating means provided adjacent said tube for heating said semiconductor wafers and impurity source so as to deposit the impurity on surfaces of said semiconductor wafers under the pressure-reduced state. 
     
     
       11. An apparatus for diffusing boron impurity into semiconductor wafers which comprises an elongated furnace tube having first and second openings, detachable closure means provided at said first opening for sealing said first opening, first supporting means for placing substantially erect semiconductor wafers into said tube to extend serially in a group along the axis of said tube, second supporting means for arranging at least one boron nitride source substantially vertically to said semiconductor wafers in said tube and spaced from, but adjacent to, the edges of said semiconductor wafers without contacting the inner surface of said tube, means connected to said second opening for reducing pressure in said tube below atmospheric pressure, and means for heating said semiconductor wafers and boron nitride source so as to deposit boron impurity on surfaces of said semiconductor wafer from the boron nitride source under the pressure-reduced state. 
     
     
       12. An apparatus according to claim 11, wherein said closure means includes means for moving said first and second supporting means inside said tube after sealing by said closure means. 
     
     
       13. An apparatus according to claim 11, wherein second detachable closure means are provided for sealing said second opening, said pressure reducing means being connected to the interior of said tube through said second closure means. 
     
     
       14. An apparatus according to claim 11, wherein said pressure reducing means reduces pressure in said tube below 100 torr. 
     
     
       15. An apparatus according to claim 14, wherein the pressure in said tube is reduced to 0.1 to 1.0 torr. 
     
     
       16. An apparatus according to claim 11, wherein said closure means provides an air-tight seal of said first opening. 
     
     
       17. An apparatus according to claim 11, wherein said semiconductor wafers are constituted of silicon. 
     
     
       18. An apparatus according to claim 11, wherein said first and second supporting means are integrally combined. 
     
     
       19. An apparatus according to claim 11, wherein said boron nitride source includes a cylinder surrounding said group of semiconductor wafers.